The production method of trihydrocarbylborane (hereinafter abbreviated as TRB) is described, for example, by taking as an example a production method of a trialkylborane.
A production method of TRB in which trialkoxyborane is reacted with trialkylaluminum is disclosed, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 47-8621) and others.B(OR)3+AlR3→BR3+Al(OR)3  (1)R: alkyl
When this reaction is carried out in industrial production, it is necessary that the by-produced trialkoxyaluminum be hydrolyzed to be separated as aluminum hydroxide, and the alcohol be recovered and then reacted with boric acid to be again converted back into a trialkoxyborane; for that purpose, equipment is to be augmented and the number of the operation steps are also to be increased; the volume of the by-product exceeds that of TRB as the target product, and hence the volume efficiency of the reaction vessel is low; further, organic liquid waste is also discharged in a large amount to necessitate the disposal thereof; from the reasons described above, the above-mentioned method is not an advantageous method for industrial production.
Another production method of TRB in which boron trihalide is reacted with trialkylaluminum is also disclosed, for example, in Patent Document 1 and others.BX3+AlR3→BR3+AlX3  (2)X=F, Cl, Br, I
In this reaction, boron trihalide as a raw material is expensive and highly toxic, and hence an industrial production of TRB based on this reaction seems to be impossible.
Patent Document 2 (U.S. Pat. No. 2,951,093) discloses a method in which boron oxide is reacted with ethylaluminum sesquichloride, and Patent Document 3 (U.S. Pat. No. 3,042,723) discloses a method in which borax is reacted with ethylaluminum sesquichloride to produce TRB; however, according to the knowledge of the present inventors, any of these is low in reaction yield, and has been evaluated not to be applicable to industrial production.
Patent Document 4 (Japanese Patent Laid-Open No. 3-258786) describes a method for obtaining TRB by reacting trialkoxyboroxine with trialkylaluminum.3R3Al+(R—O—B—O—)3→3R3B+(R—O—Al—O—)3  (3)
This reaction suffers from the by-production of an alkoxy group-containing Al compound, similarly to the reaction of (1), causing a problem of the disposal thereof. Additionally, for production of trialkoxyboroxine, a method of Patent Document 5 (Japanese Patent Publication No. SHO 41-6751) is cited; in this method, the product is obtained as a solution containing an organic solvent such as carbon tetrachloride, thus a step for separating the organic solvent and other steps are required to make this method unsuitable for industrial production.
Well known is a production method of TRB in which trialkylborane is reacted with boron oxide to yield trialkylboroxine (hereinafter abbreviated as TRBO) (reaction (4)), and then TRBO is reacted with trialkylaluminum (hereinafter abbreviated as TRAL), and thus, TRB is newly produced in twice the amount used as the raw material (reaction (5)).BR3+B2O3→R3B3O3  (4)R3B3O3+2AlR3→3BR3+Al2O3  (5)(4)+(5)BR3+B2O3+2AlR3→3BR3+Al2O3 
For example, in Non-Patent Document 1 (ORGANIC AND BIOLOGICAL CHEMISTRY, September 20, 4791 (1959)), 0.2 mole of triethylboroxine (hereinafter abbreviated as TEBO) was added and reacted with 0.4 mole of triethylaluminum (hereinafter abbreviated as TEAL), then triethylborane (hereinafter abbreviated as TEB) was obtained with a yield of 95.6%. Non-Patent Document 1 also describes that aluminum oxide becomes white crystals having satisfactory fluidity in a flask.
Patent Document 6 (U.S. Pat. No. 3,049,407) describes that for the reaction between TRBO and TRAL, the TRBO to TRAL molar ratio is preferably 2, and a reaction method of adding TRAL into TRBO is preferable; and additionally, Patent Document 6 also recommends that a tertiary amine or TEB itself be used as the dispersion medium because aluminum oxide is handled in a liquid. Further, the concerned patent discloses a continuous distillation method in which a vertical thin-film evaporator is used in the distillation and the vapor of TRB is discharged from the top of the evaporator and the solid aluminum oxide is discharged from the bottom of the evaporator.
Patent Document 1: Japanese Patent Laid-Open No. 47-8621
Patent Document 2: U.S. Pat. No. 2,951,093
Patent Document 3: U.S. Pat. No. 3,042,723
Patent Document 4: Japanese Patent Laid-Open No. 3-258786
Patent Document 5: Japanese Patent Publication No. SHO41-6751
Patent Document 6: U.S. Pat. No. 3,049,407
Non-Patent Document 1: ORGANIC AND BIOLOGICAL CHEMISTRY, September 20, 4791 (1059).